# 输入四个小数,并求平均值

a = input("第一个数字:")
b = input("第2个数字:")
c = input("第三个数字:")
d = input("第四个数字")

# d = input()



a = float(a)
b = float(b)
c = float(c)
d = float(d)

avg = (a + b + c + d) / 4
print(avg)